USP 2005/0025694 A1 has discloses a method for stably dispersing carbon nanotubes (CNTs) in an aqueous solution or oil, wherein the CNTs can be multi-walled or single-walled. According to the invention, there is no need of modifying the surface of CNTs into hydrophilic nature. The disclosed method only requires adding a selective dispersion agent and then the resulting mixture is mixed and dispersed using ultrasonic oscillation or a high shear homogenizer rotating at a high speed for achieving the objective of uniformly dispersing CNTs in the aqueous solution. A dispersion agent with an HLB value less than 8 is chosen if the CNTs are to be dispersed in oil; a dispersion agent with an HLB value greater than 10 is chosen if the CNTs are to be dispersed in the water phase.
According to CN 1667040 A1, the surfaces of CNTs are modified by at least a coupling agent selected from the group consisting of a silane coupling agent and a titanate coupling agent in an organic solvent which is selected from the group consisting of xylene, n-butanol, and cyclohexanone. After thorough mixing, the mixture is added with at least a dispersion agent selected from the group consisting of polypriopionate and modified polyurethane. After receiving an ultrasonic treatment, the mixture is uniformly dispersed in an epoxy resin by using a high speed agitation disperser. According to this modification/dispersion method, CNTs are dispersed easily, uniformly, and stably. The resulting CNT/polymer composites are a good antistatic material with good corrosion resistance, heat resistance, solvent resistance, high strength, and high adhesion.
USP 2004/0136894 A1 provides a method for dispersing CNTs in liquid or polymer, which comprises modifying the surfaces of CNTs by adding nitric acid to CNTs and refluxing the resulting mixture in 120° C. oil bath for 4 hours, so that functional groups are grafted onto the defective sites on the surfaces of the CNTs; adding a polar volatile solvent as medium to disperse the modified CNTs therein by stirring with a stirrer or ultrasonication with help from a polar force from the solvent which is able to dissolve a polymer or resin to be added; and adding the polymer or resin to the resulting dispersion, and evaporating the solvent to obtain uniform dispersion of the CNTs in the polymer or resin.
USP 2006/0058443 A1 discloses a composite material with reinforced mechanical strength by using CNTs. According to the invention, CNTs receive ultraviolet irradiation first, followed by a plasma treatment or treated with an oxidization agent, e.g. sulfuric acid or nitric acid, in order to obtain CNTs with hydrophilic groups. Subsequently, a surfactant is used to disperse the hydrophilic CNTs in a polymeric resin in order to obtain a composite material with reinforced mechanical strength by CNTs.
USP 2006/0052509 A1 discloses a method of preparing a CNT composite without adversely affecting the properties of CNTs per se. According to the invention, the surfaces of CNTs are grafted with a conductive polymer or heterocyclic trimer, which is soluble in water and contain sat least a sulfuric group and carboxylic group. The resulting CNTs are dispersed or dissolved in water, organic solvent, or organic aqueous solution after receiving ultrasonic oscillation. Even after long term storage, such a dispersion or solution will not develop agglomeration. Furthermore, such a composite material has good conductivity and film formation properties, and is easy to be coated or used as a substrate.
U.S. Pat. No. 7,090,793 discloses a composite bipolar plate of polymer electrolyte membrane fuel cells (PEMFC), which is prepared as follows: a) preparing a bulk molding compound (BMC) material containing a vinyl ester resin and a graphite powder, the graphite powder content of BMC material ranging from 60 wt % to 80 wt %, based on the compounded mixture; b) molding the BMC material from step a) to form a bipolar plate having a desired shape at 80-200° C. and 500-4000 psi, wherein the graphite powder is of 10 mesh-80 mesh. Details of the disclosure in this US patent are incorporated herein by reference.
Taiwan patent publication No. 200624604, published 16 Jul. 2006, discloses a PEMFC, which is prepared as follows: a) compounding phenolic resin and carbon fillers to form bulk molding compound (BMC) material, the BMC material containing 60 to 80 wt % graphite powder, 1 to 10 wt % carbon fiber; and one ore more conductive carbon fillers selected from: 5 to 30 wt % Ni-planted graphite powder, 2 to 8 wt % Ni-planted carbon fiber and 0.01 to 0.3 wt % carbon nanotubes, based on the weight of the phenolic resin, provided that the sum of the amounts of the carbon fiber and Ni-planted carbon fiber is not greater than 10 wt %; b) molding the BMC material from step a) to form a bipolar plates having a desired shape at 80-200° C. and 500-4000 psi. The carbon nanotubes used in this prior art are single-walled or double-walled carbon nanotubes having a diameter of 0.7-50 nm, length of 1-1000 μm, specific surface area of 40-1000 m2/g. Details of the disclosure in this Taiwan patent publication are incorporated herein by reference.
USP 2006/0267235 A1 discloses a composite bipolar plate for a PEMFC, which is prepared as follows: a) compounding vinyl ester and graphite powder to form bulk molding compound (BMC) material, the graphite powder content ranging from 60 wt % to 95 wt % based on the total weight of the graphite powder and vinyl ester, wherein carbon fiber 1-20 wt %, modified organo clay or noble metal plated modified organo clay 0.5-10 wt %, and one or more conductive fillers selected form: carbon nanotube (CNT) 0.1-5 wt %, nickel plated carbon fiber 0.5-10 wt %, nickel plated graphite 2.5-40 wt %, and carbon black 2-30 wt %, based on the weight of the vinyl ester resin, are added during the compounding; b) molding the BMC material from step a) to form a bipolar plate having a desired shaped at 80-200° C. and 500-4000 psi. Details of the disclosure in this US patent publication are incorporated herein by reference.
USP 2007/0241475 A1 discloses a composite bipolar plate for a PEMFC, which is prepared as follows: a) compounding vinyl ester and graphite powder to form bulk molding compound (BMC) material, the graphite powder content ranging from 60 wt % to 95 wt % based on the total weight of the graphite powder and vinyl ester, wherein 0.5-10 wt % modified organo clay by intercalating with a polyether amine, based on the weight of the vinyl ester resin, is added during the compounding; b) molding the BMC material from step a) to form a bipolar plates having a desired shaped at 80-200° C. and 500-4000 psi. Details of the disclosure in this US patent publication are incorporated herein by reference.
U.S. patent application Ser. No. 11/812,405, filed 19 Jun. 2007, commonly assigned to the assignee of the present application discloses TiO2-coated CNTs formed by a sol-gel method or hydrothermal method. Furthermore, the TiO2-coated CNTs are modified with a coupling agent to endow the TiO2-coated CNTs with affinity to polymer substrates. The modified TiO2-coated CNTs can be used as an additive in polymers or ceramic materials for increase the mechanical strength of the resulting composite materials. The CNT/polymer composite material prepared according to this prior art can be used to impregnate fiber cloth to form a prepreg material. Details of the disclosure in this US patent application are incorporated herein by reference.
To this date, the industry is still continuously looking for a smaller fuel cell bipolar plate having a high electric conductivity, excellent mechanical properties, a high thermal stability and a high size stability.